The present invention generally relates to a breathing circuit having a device for removing entrained water vapor from the breathing gas within the breathing circuit. More specifically, the present invention relates to a heat exchanger positioned within the breathing circuit to reduce the condensation at other areas within the breathing circuit.
A mechanical ventilator is often used to supply and remove breathing gases from a patient. The operation of the ventilator may be to assist and/or replace the natural breathing action of the patient, either alone or with the supply of an anesthetic agent to the patient. A typical mechanical ventilator has an inspiration limb for supplying breathing gases to the patient and an expiration limb for receiving breathing gases from the patient. The inspiration and expiration limbs are connected to arms of a Y-connector. A patient limb extends from a third arm of the Y-connector to an intubation tube or facemask for the subject.
A common type of mechanical ventilator recirculates the expired breathing gases from the patient through a CO2 absorber back to the inspiration limb for rebreathing by the subject. A closed breathing circuit prevents the loss of anesthetic agents to ambient air. However, the CO2 absorber in such a circuit creates an exothermic reaction that heats the breathing gas and entrains additional water vapor into the breathing gas. As an example, an additional 15 mg of water per breath become entrained in the breathing gases circulating through the CO2 absorber in the closed breathing circuit.
Although it is preferable that the patient breathe moist, warm breathing gases, the presence of vapor in the breathing circuit creates several disadvantages. Specifically, when the warm, moist breathing gases expired by the patient, which are at body temperature, pass through the breathing circuit, which is at room temperature, the water vapor in the breathing gases condenses on components of the breathing circuit. As the breathing of the patient continues, the condensed water accumulates, which may interfere with the operation of valves, sensors or other components of the breathing circuit. Additionally, the breathing gases exiting the CO2 absorber are at an elevated temperature relative to room temperature. As the breathing gases move further through the breathing circuit, the breathing gases cool and the water vapor entrained within the breathing gases can condense and accumulate within the breathing circuit.
Various solutions have been proposed to remedy this problem. Water traps may be inserted into the breathing circuit near problematic areas in an effort to accumulate water and prevent the water from reaching critical components. These water traps simply react to the problem and must be constantly monitored and emptied when the water traps become full.
Another solution is to heat the breathing circuit to prevent condensation of the water vapor. Heating of the breathing circuit may be carried out by resistance heaters, such as wires that are wrapped around the tubing of the limbs and around the sensors and valves. The heating device adds to the complexity of the breathing circuit and is often times not desired.
One specific example of a system designed to remove water vapor from breathing gases within the breathing circuit is shown and described in U.S. Pat. No. 6,619,289, the disclosure of which is incorporated herein by reference. In the '289 patent, a carbon dioxide absorber canister includes an integral moisture sump that collects condensate from areas of the breathing circuit that are difficult to drain, such as the carbon dioxide absorber canister itself.
Although the integral moisture sump within the carbon dioxide absorber canister is an effective way to remove some of the water vapor, an approach that removes additional volumes of water vapor from the breathing gas is highly desirable. Specifically, an approach that reduces the temperature of the breathing gas after the CO2 absorber without the use of any additional operating components is particularly desirable.